Coil construction



July 28, 1931. F. E. TERMAN COIL CONSTRUCTION Filed Nov. 12, 1929 5. QOM o Q 0 O O 1Q 02 Q Q 1 o 0 o 0 02 U Q o ow o as on o s 3s an 0 Q 8 6o.

I. H O 8 3 3 m" Qr g $41M ZW Patented July 28, 1931 PATENT OFFICE?FREDERICK E. TERMAN, OF STANFORD UNIVERSITY, CALIFORNIA COILCONSTBUCTICN Application filed November 12, 1929. Serial No. 406,585.

My invention relates in general to methodsof constructing coils orsolenoids and in particular to methods of constructing air coredinductance coils.

One of the objects of my invention consists in providing an improvedform of coil construction whereby the voltage rating of the coil isincreased without increasing the over all dimensions of the coil.

Another object contemplated by my invention consists in providing amethod of con- .structing air cored coils of smaller dimensions for agiven voltage rating than that hitherto possible. 7

Still another object of my invention comprises providing a methodwhereby a coil may be constructed to have a uniform volt age stress inall parts of the dielectric which separates and insulates the adjacentturns thereof.

I accomplish the above and other desirable features, which willhereinafter be pointed out and discussed, by a novel graduated spacing.of adjacent turns in single layer coils and by the graduated spacing ofadjacent turns in each layer and the relation of the layers inmulti-layer coils.

In the drawings accompanying and forming a part of this specification:

Fig. 1 illustrates diagrammatically the flux distribution in an ordinarysingle layer air cored coil or solenoid with uniform spacing betweenturns;

Figs. 2 and 2a illustrate diagrammatically a single layer air cored coilwound in accordance with my invention and show the relative spacingbetween turns;

Fig. 3 illustrates diagrammatically my improved construction method asapplied to multi-layer coils;

Fig. 4 illustrates an alternative form of applying my method ofconstruction to multi layer coils;

Fig. 5 shows graphically the distribution of the voltage stress on thedielectric between turns in the coils shown in Figs. 1, 2 and 2a.

In all single layer coils of the air cored type such as thoseillustrated in Fig. 1, the end turns of the coil, or the turns nearerthe ends of the coil, link with a smaller amount of magnetic flux thando the turns nearer the center. Inasmuch as the voltage per turn of acoil is proportional to the flux linkages per turn, it is readilyapparent that in single layer coils with uniform spacing between turnsas shown in Fig. 1, the stress on the dielectric separating turns willbe greatest at the center and least at the ends of the coil, asindicated by curve I, Fig. 5. The voltage rating of the coil isaccordingly determined by the maximum allowable voltage per turn at thecenter of the coil and with this maximum voltage the potential betweenthe outer turns is much below the maximum value that will be safe forthem. In my improved winding, I propose to make the spacing between theturns proportional to the magnetic flux linking the turn. For singlelayer coils this leads to a type of construction such as shown in Figs.Qand 2a in which the spacing between the center turns is as indicatedapproximately twice as great as that between the end turns, the spacingbetween adjacent turns progressively decreasing from the center towardsthe ends of the layer in substantially the ratio indicated. Such spacingmay, of course, be accurately determined mathematically orexperimentally by any? one skilled in the art for any type of coil underconstruction. With this construction all of the dielectric between turnsis stressed at the same voltage gradient irrespective of whether theturn is at the center or the ends of the coil, as shown by curve II,Fig. 5.

A further advantage of the type of construction shown in Fig. 2 is thatfull use is made of the insulating properties of all of the dielectricinstead of only that part of the dielectric which is at the center as inthe case of construction illustrated in Fig. 1. The consequence is thatmy proposed type of construction permits a higher voltage rating for acoil of given inductance and size than has been hitherto possible.

Viewed from another angle, my method of construction enables one toconstruct a somewhat smaller sized coil for a given voltage than wouldotherwise be possible by methods hitherto known.

Figs. 3 and 4 show the general application of my idea to multi-layercoils. In air cored coils or solenoids having more than one layer ofturns, the inner layers will not have as many flux linkages per turn asthe outer layers so that such coils hay be made with more turns perlayer as one oes to layers nearer the center. ,The individual turns ineach layer can alsobe separated from each other in accordance with thedistribution of flux linkages over the different parts of the layer.This in general means fewer turns per inch at the center of a layer thanat the ends as previously described. It is also possible to make thedistribution of the voltage gradation in the dielectric more uniform ina multi-layer coil by properly spacing the layers, making the spacingsmaller where the voltage difference between layers is at a minimum andmaking the separation between the layers larger where the voltagedifierences are considerable. The way the adjacent layers are to bearranged depends to a large extent upon how the coil is wound. Figs. 3and 4 show two cases of multi-layer coils utilizing these generalprinciples. The difference between the constructions shown in Figs. 3and 4 resides in the connections used between layers as indicated by thenumerals designating the turns, which by their numerical sequence definethe order of winding.

My method of constructing air cored coils may be applied with advantageto inductance coils used in high powered radio transmitters where thevoltage stresses between turns are sufliciently high. to make theproblem of insulation an important one. Such inductance coils are oftenrequired to handle heavy currents and their size, for that reason,becomes considerable. This increase in'size increases the necessity forgreater housing space and the magnetic flux tends to extend to greaterdistances thus interfering with the operation of adjacent apparatus. Bymy improved construction coils adapted to carry heavy currents at highvoltages may be considerably decreased in size thus simplifying theproblem of their housing andinterference with adjacent apparatus.

It will, of course, be realized that my method of coil construction isnot limited to coils used for radio purposes but applies equally well toall coils with nonmagnetic cores. Such coils or inductances are used inpower networks as current limiting reactors to limit short circuits. Bytaking advantage of my method of construction, it will be possible toreduce the size of such current limiting reactors appreciably belowtheir present dimensions without changing their voltage rating or theinductances of the coils.

Having thus completely described my invention,Iclaim: y

1. An inductance coil comprising a plurality of turns of conductorseparated by a dielectric in which the separation between turns is amaximum at the center of each layer of winding and progressivelydecreases toward the ends thereof, the separation per turn being amaximum in the outer layers of the coil and progressively decreasingtoward the axis of the coil.

2. An air cored inductance coil comprising a plurality of turns ofconductor se arated by a dielectric in-which the separation betweenturns is a maximum at the center of each layer of winding andprogressively decreases toward the ends thereof, the separation per turnbeing a maximum in the outer layers of the coil and progressivelydecreasing toward the axis of the coil. FREDERICK E. TERMAN.

